μ -oxo-galliuim phthalocyanine dimer having novel polymorph and electrophotographic photoreceptor prepared by using the same

ABSTRACT

The present invention provides μ-oxo-gallium phthalocyanine dimer having a novel polymorph. The μ-oxo-gallium phthalocyanine dimer may be applied as a charge generator for an organic photoconductive material, such as a photoreceptor of practical use and a high-gamma photoreceptor. The resulting organic photoconductive material has good stability and good electronic properties. The μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 6.8°, 12.9°, 19.0°, 19.6°, 20.3°, 25.5°, 25.9° and 26.9° in an X-ray diffraction spectrum by CuK α-ray.

FIELD OF THE INVENTION

The present invention relates to μ-oxo-gallium phthalocyanine dimerhaving a novel polymorph and an electrophotographic photoreceptorprepared by using the same.

BACKGROUND OF THE INVENTION

An electrophotographic photoreceptor have been widely applied to anelectrophotographic apparatus such as a copying machine, a printer andthe like. An inorganic photoconductor having photosensitivity in avisible region, for example amorphous selenium, has been heretofore usedas the electrophotographic photoreceptor.

However, the inorganic photoconductor has disadvantage that it containsharmful selenium and cadmium sulfide, and costs for scrapping it becomehigh. Further, the inorganic photoconductor is generally prepared by avapor deposition method, and costs for producing it become high. Thehigh production cost may also become disadvantage when it is applied toa low-priced machine.

An organic photoconductive substance which is sensitive tosemi-conductor laser ray (about 800 nm), has been therefore a matter ofinterest in the art. A lot of organic photoconductive materials usingsuch an organic photoconductive substance as an active component, havealso been proposed. Examples thereof include a negative charging-formorganic photoconductor (OPC) which contains a squarylium compound, anazulenium compound, and a phthalocyanine compound as a charge generator.This type of OPC has a conductive substrate, and a photoconductive layerformed thereon. The photoconductive layer comprises a charge generatorand a charge transporting material. The OPC is generally classified asthose of mono-layered construction and of bi-layered construction.

The conventional OPC, however, does not have sufficient electronicproperties such as chargeability, dark decay, and residual potential,and does not have sufficient durability, when it is charged andirradiated repeatedly in the practical use.

Thus, it is desired an organic photoconductive compound which has highsensitivity to visible light or longer-wavelength light, and highdurability, when it is used as a charge generator of a charge generatinglayer (CGL), particularly those of the function separated-form OPC whichhas bi-layered (CGL and charge transporting layer (CTL)) construction.

Phthalocyanine (This is hereinafter referred to as "Pc".) shows widevariety of electronic properties depending on a kind of the centralmetal atom bonded thereto, on a kind of the peripheral substituent, andon a kind of preparing process or treating process. It is also known tothe art that even if the chemical structure of Pc is equal, whenstacking state of the molecules of Pc is different, electronicproperties thereof may vary widely.

The stacking state of an organic compound is determined by a polymorphof the compound. That is, the polymorph of the compound determines anelectronic state, particularly a perturbation of π electron of thecompound. Therefore, the polymorph of the compound is an importantfactor for improving electronic properties of an organic photoconductivematerial.

Some Pcs such as titanyl Pc, vanadyl Pc, and X-form metal-free Pc areactually applied to an electrophotographic photoreceptor. JapanesePatent Kokai Publication 98181/1993, 194523/1993, 247361/1993,11873/1994, and 73303/1994, for example, describe chlorogallium Pc.Japanese Patent Kokai Publication 249716/1993, 263007/1993, and279591/1993 describe hydroxy gallium Pc having a novel polymorph.

However, photosensitivity and durability of such a conventional OPC areinsufficient. There is therefore a need for a novel polymorph of Pc,which may provide an electrophotographic photoreceptor having goodphotosensitivity and good durability.

SUMMARY OF THE INVENTION

The present invention provides μ-oxo-gallium phthalocyanine dimer havinga novel polymorph. The μ-oxo-gallium phthalocyanine dimer may be appliedto as a charge generator for an organic photoconductive material, suchas a high-gamma photoreceptor. The resulting organic photoconductivematerial has good stability and good electronic properties, that is, ithas good chargeability, small dark decay, and small residual potential.

The present invention provides the following μ-oxogallium phthalocyaninedimers having a novel polymorph, as well as the process for producingthe μ-oxo-gallium phthalocyanine dimers:

(1) μ-Oxo-gallium phthalocyanine dimer having a novel polymorph whichshows diffraction peaks at a Bragg angle (2 θ±0.2°) of 6.8°, 12.9°,19.0°, 19.6°, 20.3°, 25.5°, 25.9°, and 26.9° in an X-ray diffractionspectrum by CuK α-ray (This is hereinafter referred to as "A-formdimer".);

(2) μ-Oxo-gallium phthalocyanine dimer having a novel polymorph whichshows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.1° in an X-raydiffraction spectrum by CuK α-ray, and shows no clear peak other than7.1° (This is hereinafter referred to as "Amorphous-form dimer".);

(3) μ-Oxo-gallium phthalocyanine dimer having a novel polymorph whichshows diffraction peaks at a Bragg angle (2 θ±0.2°) of 8.1°, 8.7°, 9.2°,10.4°, 15.1°, 15.9°, 17.0°, 21.7°, 22.3°, 22.9°, 24.3°, 28.8°, 29.4°,and 30.5° in an X-ray diffraction spectrum by CuK α-ray (This ishereinafter referred to as "B-form dimer".);

(4) μ-Oxo-gallium phthalocyanine dimer having a novel polymorph whichshows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.7°, 16.0°,24.9°, and 26.3° in an X-ray diffraction spectrum by CuK α-ray (This ishereinafter referred to as "C-form dimer");

(5) μ-Oxo-gallium phthalocyanine dimer having a novel polymorph whichshows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.3°, 8.8°,22.6°, 25.5°, and 27.8° in an X-ray diffraction spectrum by CuK α-ray(This is hereinafter referred to as "D-form dimer".);

(6) μ-Oxo-gallium phthalocyanine dimer having a novel polymorph whichshows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.7°, 16.3°,24.2°, and 27.6° in an X-ray diffraction spectrum by CuK α-ray (This ishereinafter referred to as "E-form dimer".);

(7) μ-Oxo-gallium phthalocyanine dimer having a novel polymorph whichshows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.7°, 8.2°,11.1°, 12.4°, 13.3°, 15.3°, 18.5°, 18.8°, 22.1°, 22.5°, 25.5°, 27.0°,28.7°, 29.1°, and 29.4° in an X-ray diffraction spectrum by CuK α-ray(This is hereinafter referred to as "F-form dimer".);

(8) μ-Oxo-gallium phthalocyanine dimer having a novel polymorph whichshows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.4°, 9.9°,12.5°, 12.9°, 16.1°, 18.5°, 21.9°, 22.2°, 24.0°, 25.1°, 25.8°, and 28.2°in an X-ray diffraction spectrum by CuK α-ray (This is hereinafterreferred to as "G-form dimer".);

(9) μ-Oxo-gallium phthalocyanine dimer having a novel polymorph whichshows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.6°, 16.4°,25.1°, and 26.6° in an X-ray diffraction spectrum by CuK α-ray (This ishereinafter referred to as "H-form dimer".); and

(10) μ-Oxo-gallium phthalocyanine dimer having a novel polymorph whichshows diffraction peaks at a Bragg angle (2 θ±0.2°) of 6.5°, 13.1°,19.0°, 19.7°, 25.4°, and 26.3° in an X-ray diffraction spectrum by CuKα-ray (This is hereinafter referred to as "I-form dimer".).

The present invention also provides an electrophotographic photoreceptorprepared by using any one of the the μ-oxo-gallium phthalocyanine dimer.

BRIEF EXPLANATION OF DRAWINGS

FIG. 1 is an X-ray diffraction spectrum of A-form dimer, which isprepared in Example 1.

FIG. 2 is an X-ray diffraction spectrum of Amorphous-form dimer, whichis prepared in Example 2.

FIG. 3 is an X-ray diffraction spectrum of B-form dimer, which isprepared in Example 3.

FIG. 4 is an X-ray diffraction spectrum of C-form dimer, which isprepared in Example 4.

FIG. 5 is an X-ray diffraction spectrum of D-form dimer, which isprepared in Example 5.

FIG. 6 is an X-ray diffraction spectrum of E-form dimer, which isprepared in Example 6.

FIG. 7 is an X-ray diffraction spectrum of F-form dimer, which isprepared in Example 7.

FIG. 8 is an X-ray diffraction spectrum of G-form dimer, which isprepared in Example 8.

FIG. 9 is an X-ray diffraction spectrum of H-form dimer, which isprepared in Example 9.

FIG. 10 is an X-ray diffraction spectrum of I-form dimer, which isprepared in Example 10.

FIG. 11 is a FD-MS spectrum of μ-oxo-gallium phthalocyanine dimer of thepresent invention.

FIG. 12 is an X-ray diffraction spectrum of chlorogalliumphthalocyanine, which is prepared in Synthesis Example 1.

FIG. 13 is an infrared absorption spectrum of A-form dimer, which isprepared in Example 1.

FIG. 14 is an infrared absorption spectrum of Amorphous-form dimer,which is prepared in Example 2.

FIG. 15 is a plot of results obtained by a spectral response analysis ofphotoreceptors prepared in Examples 26 and 30, and Comparative Examples1 and 2.

FIG. 16 is a plot of results obtained by a surface potential durabilityanalysis of photoreceptors which is prepared in Example 26, andComparative Examples 1 and 2.

FIG. 17 is a plot of results obtained by a sensitivity durabilityanalysis of photoreceptors which is prepared in Example 26, andComparative Examples 1 and 2.

DETAILED DESCRIPTION OF THE INVENTION

μ-Oxo-gallium phthalocyanine dimer is a compound which has the followingchemical structure. ##STR1##

The μ-Oxo-gallium phthalocyanine dimer is prepared by, for example theprocess described below.

Phthalonitrile or 1,3-diiminoisoindoline is reacted with galliumchloride in a high boiling point organic solvent such as1-chloronaphthalene or quinoline to obtain chlorogallium phthalocyanine.The crude chlorogallium Pc is then purified by hot filtering, andwashing with hot DMF and DMF.

The resulting chlorogallium Pc is hydrolyzed in an acidic or an alkalinesolution, or is acid pasted by using concentrated sulfuric acid toobtain hydroxygallium Pc. The process of hydrolysis is known to the artand described in Japanese Patent Kokai Publications No. 221459/1989, and279591/1993, for example.

The wording "acid pasting by using concentrated sulfuric acid" means aprocess for finely dividing or purifying a pigment to give an amorphousstage. That is, the pigment is dissolved in concentrated sulfuric acid,preferably sulfuric acid having a concentration of not less than 90%,and the resulting solution is poured in ice water.

The resulting hydroxygallium Pc is heated and dehydrolized in awater-immiscible organic solvent having high boiling point to obtainμ-oxo-gallium Pc dimer. The hydroxygallium Pc is, for example, stirredand refluxed in o-dichlorobenzene; generated water is removed fromreaction system; the reaction product is filtered; washed with DMF; withmethanol; and dried and ground.

However, the μ-oxo-gallium Pc dimer in the present invention is preparedaccording to the following manner. That is, chlorogallium Pc is acidpasted with concentrated sulfuric acid, and then, the resulting bluesolid is heated and dehydrated in o-dichlorobenzene. ##STR2##

A-form dimer is prepared according to the above procedure. A specificpolymorph of the A-form dimer is novel.

The A-form dimer is dry milled to obtain Amorphous-form dimer.

The wording "dry mill" or "dry milling" of the present specificationmeans the procedure in which a solid substance is milled by using nosolvent. The wording "mill" or "milling" means the procedure in which asolid substance is finely divided with mechanical force. The mill ormilling is generally conducted on a dispersing machine such as a ballmill, a sand mill, a paint shaker, an attritor, and an automatic mortar,by using optionally a mill medium such as glass beads, steel beads, andalumina beads.

The dry milling is continued until change of polymorph does notprogress. It is conducted generally at room temperature for 20 to 100hours, preferably 48 to 72 hours. If the dry milling is conducted lessthan 20 hours, formation of polymorph becomes insufficient, and even ifthe dry milling is conducted more than 100 hours, useful effect may notbe obtained.

The dry milling is for example conducted by using a dispersing machine(a paint shaker for example), until polymorph of the μ-oxo-gallium Pcdimer fixes.

When 7 g of sample was used in combination with 80 g of glass beadshaving 5 mm φ, it generally takes 48 to 72 hours.

The other μ-oxo-gallium Pc dimer which has a novel polymorph of thepresent invention can be obtained by using the Amorphous-form dimer. TheAmorphous-form dimer is wet milled or simply dispersed in the specificsolvent at a raised or room temperature, to obtain the μ-oxo-gallium Pcdimer which has the specific polymorph of the present invention.

The wording "wet mill" or "wet milling" of the present specificationmeans the step in which a solid substance is milled by using a solvent.Wet milling is conducted in substantially the same manner as the drymilling, except using a solvent. Thus, a mill medium such as glassbeads, steel beads, and alumina beads may be employed in the wetmilling. The wording "simply disperse" or "simply dispersing" means thestep in which a solid substance is dispersed with stirring into asolvent.

A solvent employed in the present invention is not particularly limited,unless it solves μ-oxo-gallium phthalocyanine dimer. The solvent isselected, depending on a kind of the polymorph which is desired. It isgenerally selected from the group consisting of a ketone solvent, analcohol solvent, a glycol solvent, a formamide solvent, an amidesolvent, an ether solvent, and an aromatic solvent.

Examples of the ketone solvent include linear or cyclic ketones such ascyclohexanone, diisopropyl ketone, methyl ethyl ketone (MEK), methylisobutyl ketone (MIBK). Examples of the alcohol solvent includemonohydric lower alcohols such as methanol, ethanol, propanol,isopropanol, amyl alcohol, hexyl alcohol, and octyl alcohol. Examples ofthe glycol solvent include alkylene glycols such as ethylene glycol,diethylene glycol, triethylene glycol, and propylene glycol; alkyleneglycol monoalkyl ethers such as ethylene glycol monomethyl ether (Methylcellosolve), ethylene glycol monoethyl ether (Ethyl cellosolve), andpropylene glycol monomethyl ether; ethylene glycol dialkyl ethers suchas monoglyme, diglyme, triglyme, and tetraglyme. Examples of theformamide solvent include dimethylformamide (DMF), dimethylacetamide,and N-methyl pyrrolidone. Examples of the ether solvent include linearor cyclic ethers such as tetrahydrofuran (THF), dioxane, ethyl ether,and butyl ether. Examples of the acetate solvent include ethyl acetate,and butyl acetate. Examples of the aromatic solvent include hydrocarbonssuch as toluene, o-xylene, and tetralin, and hydrocarbons having highboiling point such as o-dichlorobenzene, chloronaphthalene,bromonaphthalene, and quinoline.

Examples of the solvent used for producing B-form dimer of the presentinvention include the glycol solvent, preferably ethylene glycol,diethylene glycol, and triethylene glycol, more preferably ethyleneglycol.

Examples of the solvent used for producing C-form dimer of the presentinvention include the ketone solvent, preferably cyclohexanone,diisopropyl ketone, more preferably cyclohexanone.

Examples of the solvent used for producing D-form dimer of the presentinvention include the alcohol solvent having not less than 5 carbonatoms, preferably amyl alcohol, hexyl alcohol, and octyl alcohol, morepreferably amyl alcohol.

Examples of the solvent used for producing E-form dimer of the presentinvention include the (poly)ethylene glycol dialkyl ethers, preferablydiglyme, triglyme, and tetraglyme, more preferably diglyme.

Examples of the solvent used for producing F-form dimer of the presentinvention include the alkylene glycol monoalkyl ethers, preferablyethylene glycol monomethyl ether, ethylene glycol monoethyl ether, andpropylene glycol monomethyl ether, more preferably ethylene glycolmonomethyl ether.

Examples of the solvent used for producing G-form dimer of the presentinvention include DMF, toluene, ethyl acetate, and triglyme, morepreferably the amide solvent such as DMF.

Examples of the solvent used for producing H-form dimer of the presentinvention include the lower ketone solvent having 3 to 10 carbon atomssuch as cyclohexanone, and methyl ethyl ketone; the lower alcoholsolvent having not more than 4 carbon atoms such as methyl alcohol, andethyl alcohol; N-methyl-2-pyrrolidone; preferably the lower ketonesolvent and the lower alcohol solvent.

The solvent is partially equal to those for producing C-, or D-formdimer. In fact, C- or D-form dimer is obtained when Amorphous-form dimeris milled or dispersed at high temperature, and H-form dimer is obtainedwhen Amorphous-form dimer is milled or dispersed at low temperature, asspecifically described below.

Examples of the solvent used for producing I-form dimer of the presentinvention include the hydrocarbons having high boiling point, preferablyo-dichlorobenzene, chloronaphthalene, bromonaphthalene, and quinoline,more preferably 1-chloronaphthalene.

The wet milling or simply dispersing is continued by using the abovedescribed specific solvent until polymorph of the μ-oxo-gallium Pc dimerfixes. It takes generally for 5 to 50 hours, preferably 10 to 20 hoursat from room temperature up to reflux temperature of the solvent. If thestep is conducted less than 5 hours, formation of the polymorph becomesinsufficient, and even if the step is conducted more than 50 hours,useful effect may not be obtained.

When ethylene glycol is used as the solvent, Amorphous-form dimer is wetmilled at room temperature for about 16 hours to obtain B-form dimer ofthe present invention.

When cyclohexanone is used as the solvent, Amorphous-form dimer issimply dispersed with refluxing for about 30 to 40 hours to obtainC-form dimer of the present invention.

When amyl alcohol is used as the solvent, Amorphous-form dimer is simplydispersed with refluxing for about 10 hours to obtain D-form dimer ofthe present invention.

When diglyme is used as the solvent, Amorphous-form dimer is simplydispersed with refluxing for about 24 hours to obtain E-form dimer ofthe present invention.

When ethylene glycol monomethyl ether is used as the solvent,Amorphous-form dimer is simply dispersed with refluxing for about 13hours to obtain F-form dimer of the present invention.

When DMF is used as the solvent, Amorphous-form dimer is simplydispersed at room temperature for about 10 to 12 hours to obtain G-formdimer of the present invention.

When cyclohxanone or lower alcohol is used as the solvent,Amorphous-form dimer is simply dispersed or is wet milled at roomtemperature for about 8 hours to obtain H-form dimer of the presentinvention.

When 1-chloronaphthalene is used as the solvent, Amorphous-form dimer issimply dispersed with refluxing for about 15 to 30 hours to obtainI-form dimer of the present invention.

μ-Oxo-gallium Pc dimer having a novel polymorph of the present inventionis preferably employed as a photoconductive material for use in anelectrophotographic photoreceptor which is widely applied to a copyingmachine using electrophotographic technology.

The photoconductive material comprising μ-oxo-gallium Pc dimer of thepresent invention as an effective ingredient provides goodchargeability, high sensitivity, and high durability, when it is appliedas a charge generating layer of an electrophotographic receptor.

The electrophotographic receptor generally has a conductive substrate,and a photoconductive layer formed thereon which comprises a chargegenerator and a charge transporting material. The photoconductive layermay be classified depending on its structure, i.e., a mono-layered oneand a bi-layered one. μ-Oxo-gallium Pc dimer of the present inventionmay be employed in both the mono-layered photoconductive layer and thebi-layered photoconductive layer.

However, it is preferred that μ-oxo-gallium Pc dimer of the presentinvention is applied to the bi-layered photoconductive layer becauseeach of the layers in the bi-layered photoconductive layer do notinhibit the respective functions, and they efficiently transfer thegenerated charge to a surface of the electrophotographic photoreceptorwithout trapping the charge, and therefore, electronic properties of theμ-oxo-gallium Pc dimer may sufficiently be exhibited. Theelectrophotographic photoreceptor which has bi-layered construction isgenerally called as a function separated-form photoreceptor.

The function separated-form photoreceptor is prepared by, for example,forming a charge generating layer on a conductive substrate, and forminga charge transporting layer thereon. Examples of the conductivesubstrate include metal (e.g., aluminium, nickel), metal vapor-depositedfilm and the like, in the form of a drum, a sheet or a belt.

μ-Oxo-gallium Pc dimer of the present invention may be included as acharge generator in the charge generating layer. The charge generatinglayer is formed as a thin layer on the conductive substrate. It can beformed by vapor-depositing the μ-oxo-gallium Pc dimer, but is generallyformed by applying a binder resin dispersion of the μ-oxo-gallium Pcdimer. The binder resin dispersion may be prepared by dispersing theμ-oxo-gallium Pc dimer into a solution of a suitable binder resin, usinga usual dispersing apparatus such as a ball mill, a sand mill, a paintshaker and the like.

A process for coating the binder resin dispersion is not specificallylimited, and suitably include bar coating, dip coating, spin coating,roller coating, calendar coating and the like. The coated layer may bedried at a temperature of 30 to 200° C. for 5 minutes to 2 hours in thepresence or absence of blast.

A solvent optionally be employed for preparing the dispersion. Thesolvent employed in the present invention is not particularly limitedunless it solves μ-oxo-gallium Pc dimer. However, a solvent which maydisperse μ-oxo-gallium Pc dimer uniformly and may solve the binderresin, is preferred. Examples thereof include alcohol solvents such asmethanol, ethanol, isopropanol, and butanol; aromatic solvents such astoluene, xylene and tetralin; halogenated solvents such asdichloromethane, chloroform, trichloroethylene and carbon tetrachloride;ester solvents such as ethyl acetate and propyl acetate; ether solventssuch as ethylene glycol monoethyl ether, dioxane and tetrahydrofuran;dimethylformamide and dimethyl sulfoxide.

The binder resin can be selected from a wide range of insulating resins.Examples of the preferred resin include condensation resins such aspolycarbonate, polyester, polyamide, and polyallylate; addition polymerssuch as polystyrene, polyacrylate, styrene-acrylic copolymer,polyacrylamide, polymethacrylate, polyvinyl butyral, polyvinyl alcohol,polyacrylonitrile, polyacrylic-butadiene copolymer, polyvinyl chlorideand vinyl chloride-vinyl acetate copolymer; organic photoconductiveresins such as poly-N-vinyl carbazole and polyvinylanthracene;polysulfone, polyether sulfone, silicone resin, epoxy resin and urethaneresin. These are used alone or in combination thereof.

The binder resin is employed in an amount of from 0.1 to 3.0 ratio byweight, preferably 0.5 to 2.0 by weight based on the charge generator.When the amount is more than 3.0, the amount of charge decreases, andsensitivity of the photoconductive layer becomes poor. The chargegenerating layer is preferably formed in a thickness of from 0.05 to 5.0μm, preferably 0.1 to 3.0 μm. When the thickness is more than 5.0 μm,charge may readily be trapped, and sensitivity of the photoconductivelayer becomes poor.

A charge transporting layer containing a charge transporting material isthen formed on the charge generating layer. This layer may be formed inthe same manner as described above, for forming the charge generatinglayer. That is, the charge transporting material is dissolved in asolvent with a binder resin, and the resulting solution is uniformlyapplied on the charge generating layer, followed by drying.

Examples of the charge transporting material include conventionalmaterials such as an oxadiazole derivative, a pyrazoline derivative, ahydrazone derivative, a triazine derivative, a quinazoline derivative, atriarylamine compound, a styryltriphenylamine compound, a butadienecompound, and a carbazole compound.

Examples of the binder resin and solvent include the same materials asthat employed for the charge generating layer.

The binder resin is employed in an amount of from 0.1 to 5.0 ratio byweight, preferably 0.5 to 2.0 ratio by weight based on the chargetransporting material. When the amount is more than 5.0, concentrationof the charge transporting material in the charge transporting layerbecomes small, and sensitivity of the photoconductive layer becomespoor. The charge transporting layer is preferably formed in a thicknessof from 5 to 50 μm, preferably 10 to 40 μm. When the thickness is morethan 50 μm, long time is required for transporting the charge, and thecharge may readily be trapped, and thereby sensitivity of thephotoconductive layer becomes poor.

EXAMPLES

The following Examples and Comparative Examples further illustrate thepresent invention in detail but are not to be construed to limit thescope thereof.

The X-ray diffraction spectrum by CuK α-ray was measured by using theautomatic X-ray diffraction system "MXP3" manufactured by Max ScienceCo. Ltd.

Synthesis Example 1

Synthesis of chlorogallium Pc

177.2 g of phthalonitrile, 820 ml of 1-chloronaphthalene, and 50.0 g ofgallium chloride were charged in a 1000 ml glass four-necked flaskequipped with requisite apparatuses such as a stirrer, a calciumchloride tube and the like, and the mixture was refluxed with stirringfor 10 hours. Heating was then stopped and the mixture was cooled toabout 200° C., and hot filtered and washed with 3500 ml of hot DMF, and3000 ml of DMF.

The resulting wet cake was dispersed in 800 ml of DMF, and refluxed withstirring for 5 hours. The mixture was hot filtered, and washed againwith 2500 ml of hot DMF and 2000 ml of DMF. The DMF was then replacedwith methanol, and the product was dried to obtain 125.0 g of blue solidchlorogallium Pc (yield 73.5%). An X-ray diffraction spectrum of theproduct was shown in FIG. 12. The results of elemental analysis wereshown in Table 1.

                  TABLE 1    ______________________________________            C       H      N        Cl   Ga    ______________________________________    Calculated %              62.22     2.61   18.14  5.74 11.29    Found %   62.23     2.52   18.02  6.04 10.39    ______________________________________

Example 1

Synthesis of A-form dimer

10.0 g of chlorogallium Pc prepared in Synthesis Example 1was slowlyadded to 300 g of sulfonic acid, with controlling a temperature thereofbetween 0 to 5° C., and the mixture was stirred for 1 hour. The mixturewas then poured into 1500 ml of ice water with stirring and withcontrolling a temperature thereof not more than 5° C., and stirred for 2hours. The resulting mixture was filtered and washed with water, and wasdispersed in 1500 ml of ion exchanged water, and filtered again. The wetcake was washed with water, dispersed in 600 ml of 4% aqueous ammonia,and stirred with refluxing for 6 hours. The product was filtered again,and the resulting cake was thoroughly washed with water, dried undervacuum at 50° C., and ground to obtain 8.72 g of blue solidhydroxygallium Pc (yield 89.8%).

7.7 g of the hydroxygallium Pc was added to 130 ml of o-dichlorobenzene,and the mixture was stirred at a temperature between 170 to 180° C. Thewater which was generated was removed through Liebig condenser equippedbeforehand. When generation of water stopped, the Liebig condenser wasreplaced with an air cooling condenser, the mixture was refluxed withstirring for 3 hours, and hot filtered. The cake was washed with DMF,and then with methanol in order to remove DMF. The product was dried,and ground to obtain 7.1 g of μ-oxo-gallium Pc dimer (yield 93.6%).

The μ-oxo-gallium Pc dimer had the polymorph which shows diffractionpeaks at a Bragg angle (2 θ±0.2°) of 6.8°, 12.9°, 19.0°, 19.6°, 20.3°,25.5°, 25.9°, and 26.9°, as shown in FIG. 1. Thus, it is A-form dimer.

An infrared absorption spectrum of the product was shown in FIG. 13. AnFD-MS spectrum of the product was shown in FIG. 11. In FIG. 11,horizontal axis represents M/Z (ratio of mass to electric charge), andvertical axis represents relative abundance. A peak of μ-oxo-gallium Pcdimer is present at M/Z=1180 M+H!⁺ of the FD-MS spectrum.

Conditions for FD-MS analysis (Field Desorption-MS) is shown in Table 2.

TABLE 2

Apparatus: MS:JVS-DX303HF (manufactured by JEOL K.K.)

Conditions: FD method by using a carbon emitter

Resolution: 1500, or 500; 35 to 1700 M/Z

Accelerating voltage: 2.5 kV

Ion multiplier voltage: 1.6 to 1.8 kV

Emitter current: 0 to 40 mA

Cathode voltage: 5.0 kV

Solvent: DMF

The results of elemental analysis were shown in Table 3.

                  TABLE 3    ______________________________________            C       H      N        Cl   Ga    ______________________________________    Calculated %              65.12     2.73   18.98  --   11.81    Found %   65.07     2.64   18.80  --   10.75    ______________________________________

Example 2

Synthesis of Amorphous-form dimer

7.0 g of A-form dimer prepared in Example 1, and 80 g of glass beadshaving a diameter of 5 mm φ were charged in a wide-mouthed bottle, andthe mixture was dry milled for 2 to 3 days using a dispersing apparatus(paint shaker). The polymorph of the mixture was followed by sampling apart of the mixture. When the polymorph fixed, the glass beads werefiltered out, and 6.8 g of blue solid μ-oxo-gallium Pc dimer wasobtained.

An X-ray diffraction spectrum of the product was shown in FIG. 2, aninfrared absorption spectrum was shown in FIG. 14, and the result ofFD-MS analysis was shown in FIG. 11. Further, the results of elementalanalysis were shown in Table 4.

                  TABLE 4    ______________________________________            C       H      N        Cl   Ga    ______________________________________    Calculated %              65.12     2.73   18.98  --   11.81    Found %   65.68     2.71   18.58  --   10.80    ______________________________________

The above described results show that the product is μ-oxo-gallium Pcdimer, and the X-ray diffraction spectrum indicates that theμ-oxo-gallium Pc dimer is Amorphous-form dimer which shows diffractionpeak at a Bragg angle (2 θ±0.2°) of 7.1°, and shows no clear peak otherthan 7.1°.

Example 3

Synthesis of B-form dimer

1.0 g of Amorphous-form dimer prepared in Example 2 was added to 30 mlof ethylene glycol, and the mixture was wet milled at room temperaturefor about 16 hours, by using paint shaker. The mixture was filtered. Theresulting wet cake was washed with with DMF, and then with methanol inorder to remove DMF. The product was dried under vacuum to obtain 0.96 gof blue solid μ-oxo-gallium Pc dimer.

An X-ray diffraction spectrum of the product was shown in FIG. 3. Theresult of FD-MS analysis was shown in FIG. 11. Further, the results ofelemental analysis were shown in Table 5.

                  TABLE 5    ______________________________________            C       H      N        Cl   Ga    ______________________________________    Calculated %              65.12     2.73   18.98  --   11.81    Found %   65.90     3.54   16.90  --    9.89    ______________________________________

The above described results show that the product is μ-oxo-gallium Pcdimer, and the X-ray diffraction spectrum indicates that theμ-oxo-gallium Pc dimer is B-form dimer which shows diffraction peaks ata Bragg angle (2 θ±0.2°) of 8.1°, 8.7°, 9.2°, 10.4°, 15.1°, 15.9°,17.0°, 21.7°, 22.3°, 22.9°, 24.3°, 28.8°, 29.4°, and 30.5°.

Example 4

Synthesis of C-form dimer

1.0 g of Amorphous-form dimer prepared in Example 2 was added to 30 mlof cyclohexanone, and the mixture was refluxed with stirring (simplydispersed) for 30 to 40 hours. The mixture was allowed to cool, andfiltered. The resulting wet cake was washed with methanol and driedunder vacuum to obtain 0.61 g of blue solid μ-oxo-gallium Pc dimer.

An X-ray diffraction spectrum of the product was shown in FIG. 4. Theresult of FD-MS analysis was shown in FIG. 11. Further, the results ofelemental analysis were shown in Table 6.

                  TABLE 6    ______________________________________            C       H      N        Cl   Ga    ______________________________________    Calculated %              65.12     2.73   18.98  --   11.81    Found %   65.72     3.48   14.97  --   10.64    ______________________________________

The above described results show that the product is μ-oxo-gallium Pcdimer, and the X-ray diffraction spectrum indicates that theμ-oxo-gallium Pc dimer is C-form dimer which shows diffraction peaks ata Bragg angle (2 θ±0.2°) of 7.7°, 16.0°, 24.9°, and 26.3°.

Example 5

Synthesis of D-form dimer

1.0 g of Amorphous-form dimer prepared in Example 2 was added to 30 mlof amyl alcohol, and the mixture was refluxed with stirring (simplydispersed) for 10 hours. The mixture was allowed to cool, and filtered.The resulting wet cake was washed with methanol and dried under vacuumto obtain 0.91 g of blue solid μ-oxo-gallium Pc dimer.

An X-ray diffraction spectrum of the product was shown in FIG. 5. Theresult of FD-MS analysis was shown in FIG. 11. Further, the results ofelemental analysis were shown in Table 7.

                  TABLE 7    ______________________________________            C       H      N        Cl   Ga    ______________________________________    Calculated %              65.12     2.73   18.98  --   11.81    Found %   66.15     4.03   16.97  --    9.90    ______________________________________

The above described results show that the product is μ-oxo-gallium Pcdimer, and the X-ray diffraction spectrum indicates that theμ-oxo-gallium Pc dimer is D-form dimer which shows diffraction peaks ata Bragg angle (2 θ±0.2°) of 7.3°, 8.8°, 22.6°, 25.5°, and 27.8°

Example 6

Synthesis of E-form dimer

1.0 g of Amorphous-form dimer prepared in Example 2 was added to 30 mlof diglyme, and the mixture was refluxed with stirring (simplydispersed) for 24 hours. The mixture was allowed to cool, and filtered.The resulting wet cake was washed with methanol and dried under vacuumto obtain 0.60 g of blue solid μ-oxo-gallium Pc dimer.

An X-ray diffraction spectrum of the product was shown in FIG. 6. Theresult of FD-MS analysis was shown in FIG. 11. Further, the results ofelemental analysis were shown in Table 8.

                  TABLE 8    ______________________________________            C       H      N        Cl   Ga    ______________________________________    Calculated %              65.12     2.73   18.98  --   11.81    Found %   66.60     2.87   18.50  --   10.60    ______________________________________

The above described results show that the product is μ-oxo-gallium Pcdimer, and the X-ray diffraction spectrum indicates that theμ-oxo-gallium Pc dimer is E-form dimer which shows diffraction peaks ata Bragg angle (2 θ±0.2°) of 7.7°, 16.3°, 24.2°, and 27.6°.

Example 7

Synthesis of F-form dimer

1.0 g of Amorphous-form dimer prepared in Example 2 was added to 30 mlof ethylene glycol monomethyl ether, and the mixture was refluxed withstirring (simply dispersed) for 13 hours. The mixture was allowed tocool, and filtered. The resulting wet cake was washed with methanol anddried under vacuum to obtain 0.88 g of blue solid μ-oxo-gallium Pcdimer.

An X-ray diffraction spectrum of the product was shown in FIG. 7. Theresult of FD-MS analysis was shown in FIG. 11. Further, the results ofelemental analysis were shown in Table 9.

                  TABLE 9    ______________________________________            C       H      N        Cl   Ga    ______________________________________    Calculated %              65.12     2.73   18.98  --   11.81    Found %   67.07     3.29   17.76  --   10.35    ______________________________________

The above described results show that the product is μ-oxo-gallium Pcdimer, and the X-ray diffraction spectrum indicates that theμ-oxo-gallium Pc dimer is F-form dimer which shows diffraction peaks ata Bragg angle (2 θ±0.2°) of 7.7°, 8.2°, 11.1°, 12.4°, 13.3°, 15.3°,18.5°, 18.8°, 22.1°, 22.5°, 25.5°, 27.0°, 28.7°, 29.1°, and 29.4°.

Example 8

Synthesis of G-form dimer

1.0 g of Amorphous-form dimer prepared in Example 2 was added to 30 mlof DMF, and the mixture was stirred (simply dispersed) at roomtemperature for 10 to 12 hours. The mixture was allowed to cool, andfiltered. The resulting wet cake was washed with methanol and driedunder vacuum to obtain 0.84 g of blue solid μ-oxo-gallium Pc dimer.

An X-ray diffraction spectrum of the product was shown in FIG. 8. Theresult of FD-MS analysis was shown in FIG. 11. Further, the results ofelemental analysis were shown in Table 10.

                  TABLE 10    ______________________________________            C       H      N        Cl   Ga    ______________________________________    Calculated %              65.12     2.73   18.98  --   11.81    Found %   63.76     2.85   18.65  --   10.07    ______________________________________

The above described results show that the product is μ-oxo-gallium Pcdimer, and the X-ray diffraction spectrum indicates that theμ-oxo-gallium Pc dimer is G-form dimer which shows diffraction peaks ata Bragg angle (2 θ±0.2°) of 7.4°, 9.9°, 12.5°, 12.9°, 16.1°, 18.5°,21.9°, 22.2°, 24.0°, 25.1°, 25.8°, and 28.2°.

Example 9

Synthesis of H-form dimer

1.0 g of Amorphous-form dimer prepared in Example 2 was added to 30 mlof cyclohexanone, and the mixture was stirred (simply dispersed) at roomtemperature for 8 hours. The mixture was allowed to cool, and filtered.The resulting wet cake was washed with methanol and dried under vacuumto obtain 0.97 g of blue solid μ-oxo-gallium Pc dimer.

An X-ray diffraction spectrum of the product was shown in FIG. 9. Theresult of FD-MS analysis was shown in FIG. 11. Further, the results ofelemental analysis were shown in Table 11.

                  TABLE 11    ______________________________________            C       H      N        Cl   Ga    ______________________________________    Calculated %              65.12     2.73   18.98  --   11.81    Found %   64.56     3.20   17.95  --   10.39    ______________________________________

The above described results show that the product is μ-oxo-gallium Pcdimer, and the X-ray diffraction spectrum indicates that theμ-oxo-gallium Pc dimer is H-form dimer which shows diffraction peaks ata Bragg angle (2 θ±0.2°) of 7.6°, 16.4°, 25.1°, and 26.6°.

Example 10

Synthesis of I-form dimer

1.0 g of Amorphous-form dimer prepared in Example 2 was added to 30 mlof 1-chloronaphthalene, and the mixture was refluxed with stirring(simply dispersed) for 10 to 15 hours. The mixture was allowed to cool,and filtered. The resulting wet cake was washed with methanol and driedunder vacuum to obtain 0.86 g of blue solid μ-oxo-gallium Pc dimer.

An X-ray diffraction spectrum of the product was shown in FIG. 10. Theresult of FD-MS analysis was shown in FIG. 11. Further, the results ofelemental analysis were shown in Table 12.

                  TABLE 12    ______________________________________            C       H      N        Cl   Ga    ______________________________________    Calculated %              65.12     2.73   18.98  --   11.81    Found %   64.68     2.71   18.58  --   10.80    ______________________________________

The above described results show that the product is μ-oxo-gallium Pcdimer, and the X-ray diffraction spectrum indicates that theμ-oxo-gallium Pc dimer is I-form dimer which shows diffraction peaks ata Bragg angle (2 θ±0.2°) of 6.5°, 13.1°, 19.0°, 19.7°, 25.4°, and 26.3°.

The experimental process described in Examples 1 to 10 was summarized inthe following Table 13.

                                      TABLE 13    __________________________________________________________________________    Ex.       Original     Condition       Resultant    No.       polymor..sup.1)            Solvent Temp(°C.)                         Time Procedure                                    polymor.    __________________________________________________________________________    1  C1-GaPc.sup.2)            --      --   --   --    A    2  A    --      ca. room                         2-3 d                              dry mill                                    Amorph.    3  Amorph.            Ethylene                    room 16 h wet mill                                    B            glycol    4  Amorph.            Cyclohexanone                    reflux                         30-40 h                              simply disp.                                    C    5  Amorph.            Amyl alcohol                    reflux                         10 h simply disp.                                    D    6  Amorph.            Diglyme reflux                         24 h simply disp.                                    E    7  Amorph.            Methyl  reflux                         13 h simply disp.                                    F            cellosolve    8  Amorph.            DMF     room 10-12 h                              simply disp.                                    G    9  Amorph.            Cyclohexanone                    room 8 h  simply disp.                                    H    10 Amorph.            1-Chloro-                    reflux                         12-15 h                              simply disp.                                    I            naphthalene    __________________________________________________________________________     .sup.1) Polymorph of oxo-gallium Pc dimer.     .sup.2) Chlorogallium Pc

Examples 11 to 13

The present examples illustrate a function separated-formelectrophotographic photoreceptor to which the μ-oxo-gallium Pc dimerhaving a novel polymorph of the present invention was applied. Theμ-oxo-gallium Pc dimers prepared in Examples were employed as a chargegenerator (CG material).

Example 11

0.2 g of A-form dimer, 0.2 g of a polyvinyl butyral resin ("ELEX BH-3"available from Sekisui Kagaku K. K.), 59.6 g of cyclohexanone, and 50 gof glass beads having a diameter of 3 mmφ were charged in a wide-mouthedbottle. The mixture was shook for 1 hour using a dispersing apparatus(paint shaker), and applied on an aluminum plate by a bar coater. Thecoating was dried in air to form a charge generating layer having athickness of 0.5 μm.

1.5 g of 1,1-bis(p-diethylaminophenyl)-4,4'-diphenyl-1,3-butadiene("T-405" available from Takasa Koryo K. K.), 1.5 g of a polycarbonateresin ("PANLIGHT L-1250" available from Teijin K. K.), and 57.0 g ofmethylene chloride were charged in a wide-mouthed bottle. The mixturewas homogenized by using supersonic wave, and applied on the chargegenerating layer by a bar coater. The coating was dried in air to form acharge transporting layer having a thickness of 20 μm. Thereby, abi-layered electrophotographic photoreceptor was prepared.

Example 12

An electrophotographic photoreceptor was prepared according tosubstantially the same manner as described in Example 11, except that4-benzylamino-2-methylbenzaldehyde-1,1'-diphenylhydorazone ("CTC-191"manufactured by Takasa Koryo K.K.) was used as a CT material instead of1,1-bis(diethylaminophenyl)-4,4'-diphenyl-1,3-butadiene.

Example 13

An electrophotographic photoreceptor was prepared according tosubstantially the same manner as described in Example 11, except thatthe Amorphous-form dimer was used as a CG material instead of A-formdimer.

Examples 14 to 30

Electrophotographic photoreceptors of the present invention wereprepared according to substantially the same manner as described inExample 11, except that the materials tabulated in the following Table14 were used as a CG material and a CT material.

Comparative Example 1

An electrophotographic photoreceptor was prepared according tosubstantially the same manner as described in Example 12, except thatY-form titanyl Pc which was prepared according to the proceduredescribed in Japanese Patent Kokoku Publication No. 35064/1991 (KonicaK. K.) was used as a CG material instead of A-form dimer.

Comparative Example 2

An electrophotographic photoreceptor was prepared according tosubstantially the same manner as described in Example 12, except thatX-form metal-free Pc which was prepared according to the proceduredescribed in Japanese Patent Kokoku Publication No. 78872/1991 was usedas a CG material instead of A-form dimer.

Comparative Example 3

An electrophotographic photoreceptor was prepared according tosubstantially the same manner as described in Example 12, except thatchlorogallium Pc which was prepared in Synthesis Example 1 was used as aCG material instead of A-form dimer.

Evaluation of Property of the Photoreceptors

Electrophotographic property of the photoconductors prepared in Examples11 to 30 and Comparative Examples 1 to 3 were measured. A staticelectricity charging tester "EPA-8200" manufactured by Kawaguchi DenkiK. K. was used as the measuring apparatus.

The sample was corona charged at-8.0 kV in STAT 3 mode by first. It wasthen left in the dark for 20 seconds, and irradiated by 5.0 lux whitelight for 10.0 seconds. The charged potential (Vo), the sensitivityhalf-value irradiation amount (E_(1/2)), the residual potential (Vr)were recorded. The results were shown in Table 14.

                                      TABLE 14    __________________________________________________________________________    Ex.       CG material           V.sub.o                                E.sub.1/2                                      Vr    No.       (Polymorph)             Solvent.sup.1)                       CT material                             (V)                                (Lux · sec)                                      (V)    __________________________________________________________________________    11 A     --        T-405 -196                                4.97  -4.3    12 A     --        CTC-191                             -259                                6.40  -6.7    13 Amorphous             --        T-405 -120                                2.04  -4.7    14 Amorphous             --        CTC-191                             -160                                4.09  -1.3    15 B     Ethylene glycol                       T-405 -175                                4.06  -5.0    16 B     Ethylene glycol                       CTC-191                             -237                                --    -8.3    17 C     Cyclohexanone                       T-405 -189                                7.46  -5.3    18 C     Cyclohexanone                       CTC-191                             -239                                18.55 -38.0    19 D     Amyl alcohol                       T-405 -139                                1.94  -5.3    20 D     Amyl alcohol                       CTC-191                             -194                                6.05  -4.0    21 E     Diglyme   T-405 -234                                5.89  -4.7    22 E     Diglyme   CTC-191                             -248                                9.54  -12.3    23 F     Methyl cellosolve                       T-405 -195                                5.47  -3.7    24 F     Methyl cellosolve                       CTC-191                             -234                                --    -12.7    25 G     DMF       T-405 -132                                0.82  -5.7    26 G     DMF       CTC-191                             -218                                1.51  -1.3    27 H     Cyclohexanone                       T-405 -185                                3.56  -5.0    28 H     Cyclohexanone                       CTC-191                             -232                                8.42  -5.0    29 I     1-Chloronaphthalene                       T-405 -137                                2.18  -5.0    30 I     1-Chloronaphthalene                       CTC-191                             -184                                3.13   0.0    C1 Ti Pc.sup.2)             --        CTC-191                             -173                                1.09  -2.0    C2 H2-Pc.sup.3)             --        T-405 -195                                4.09  -2.0    C3 C1-GaPc.sup.4)             --        CTC-191                             -240                                8.29  -7.7    __________________________________________________________________________     .sup.1) Solvent which is used for the development of the corresponding     polymorph.     .sup.2) Titanyl Pc     .sup.3) Xform nonmetalloPc     .sup.4) Chlorogallium Pc     T405: 1,1bis(p-diethylaminophenyl)-4,4'-diphenyl1,3-butadiene available     from Takasa Koryo K.K.     CTC191: 4benzylamino-2-methylbenzaldehyde-1,1'-diphenylhydorazone     manufactured by Takasa Koryo K.K.     --: impossible to measure

Example 31

Four bi-layered electrophotographic photoreceptors were preparedaccording to substantially the same manner as described in Example 11,except that G-form dimer of Example 26, I-form dimer of Example 30,Y-form titanyl Pc of Comparative Example 1, and X-form metal-free Pc ofComparative Example 2, were used as a CG material respectively.

The resulting electrophotographic photoreceptors were charged, accordingto substantially the same manner as described in the column of"Evaluation of Property of the Photoreceptors", except that amonochlomic light having a wavelength of 450 nm through a band pathinterference filter, was irradiated. Energy for irradiation wascontrolled to 1.00 μW.

The initial charged potential (V_(max) V!), and the sensitivityhalf-value irradiation amount (E_(1/2) μJ/cm² !) were measured.

A wavelength of the monochromic light was controlled at an interval of50 nm between from 450 to 900 nm, and the above described measurementwas repeated. The resulting spectroscopic sensitivities of theelectrophotographic photoreceptors were plotted. The results were shownin FIG. 15.

Three bi-layered electrophotographic photoreceptors were preparedaccording to substantially the same manner as described in Example 11,except that G-form dimer of Example 26, Y-form titanyl Pc of ComparativeExample 1, and X-form metal-free Pc of Comparative Example 2, were usedas a CG material respectively.

A static electricity charging tester "EPA-8200" was set to the mode formeasuring durability. The electrophotographic photoreceptors were thencharged, according to substantially the same manner as described in thecolumn of "Evaluation of Property of the Photoreceptors". The chargingand discharging were repeated 100 times, on the mode for measuringdurability of the static electricity charging tester. Change of chargedpotential (Vo), and sensitivity half-value irradiation amount (E_(1/2))during the repetition of charging and discharging, was measured, withrespect to each electrophotographic photoreceptors. The results wereshown in FIG. 16 and 17.

The photoreceptors which employ the D-, E-, F-, G-, and I-form dimershow particularly high photoconductivity, and those which employ the G-,and I-form dimer also show good reproductivity. On the other hand, theComparative Examples which employ the conventional CG materials such asY-form titanyl Pc and X-form metal-free Pc, show poor photosensitiveproperties.

The μ-oxo-gallium Pc dimer having novel polymorph of the presentinvention achieves high sensitivity half-value irradiation amount bycomparison with X-form metal-free Pc, and achieves excellent durabilityby comparison with Y-form titanyl Pc. As a result, μ-oxo-gallium Pcdimer having novel invention of the present invention is useful as aphotoconductive materials for use in the related art of optoelectronics.

The inventors are now further investigating a binder and a CT materialwhich well match with the μ-oxo-gallium Pc dimer of the presentinvention.

What is claimed is:
 1. An electrophotographic photoreceptor which includes an μ-oxo-gallium phthalocyanlne dimer as a charge generator, wherein said μ-oxo-gallium phthalocyanine dimer is selected from the group consisting of:a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 6.8°, 12.9°, 19.0°, 19.6°, 20.3°, 25.5°, 25.9°, and 26.9° in an X-ray diffraction spectrum by CuK α-ray (A-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.1° in an X-ray diffraction spectrum by CuK α-ray, and shows no clear peak other than 7.1° (Amorphous-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 8.1°, 8.7°, 9.2°, 10.4°, 15.1°, 15.9°, 17.0°, 21.7°, 22.3°, 22.9°, 24.3°, 28.8°, 29.4°, and 30.5° in an X-ray diffraction spectrum by CuK α-ray (B-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.7°, 16.0°, 24.9°, and 26.3° in an X-ray diffraction spectrum by CuK α-ray (C-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.3°, 8.8°, 22.6°, 25.5°, and 27.8° in an X-ray diffraction spectrum by CuK α-ray (D-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.7°, 16.3°, 24.2°, and 27.6° in an X-ray diffraction spectrum by CuK α-ray (E-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.7°, 8.2°, 11.1°, 12.4°, 13.3°, 15.3°, 18.5°, 18.8°, 22.1°, 22.5°, 25.5°, 27.0°, 28.7°, 29.1°, and 29.4° in an X-ray diffraction spectrum by CuK α-ray (F-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.4°, 9.9°, 12.5°, 12.9°, 16.1°, 18.5°, 21.9°, 22.2°, 24.0°, 25.1°, 25.8°, and 28.2° in an X-ray diffraction spectrum by CuK α-ray (G-form), a μ-oxo-gailium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.6°, 16.4°, 25.1°, and 26.6° in an X-ray diffraction spectrum by CuK α-ray (H-form), and a μ-oxo-gailium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 6.5°, 13.1°, 19.0°, 19.7°, 25.4°, and 26.3° in an x-ray diffraction spectrum by CuK α-ray (I-form).
 2. The electrophotographic photoreceptor according to claim 1, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 6.8°, 12.9°, 19.0°, 19.6°, 20.3°, 25.5°, 25.9°, and 26.9° in an X-ray diffraction spectrum by CuK α-ray (A-form).
 3. The electrophotographic photoreceptor according to claim 1, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.1° in an X-ray diffraction spectrum by CuK α-ray, and shows no clear peak other than 7.1° (Amorphous-form).
 4. The electrophotographic photoreceptor according to claim 1, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 8.1°, 8.7°, 9.2°, 10.4°, 15.1°, 15.9°, 17.0°, 21.7°, 22.3°, 22.9°, 24.3°, 28.8°, 29.4°, and 30.5° in an X-ray diffraction spectrum by CuK α-ray (B-form).
 5. The electrophotographic photoreceptor according to claim 1, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.7°, 16.0°, 24.9°, and 26.3° in an X-ray diffraction spectrum by CuK α-ray (C-form).
 6. The electrophotographic photoreceptor according to claim 1, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.3°, 8.8°, 22.6°, 25.5°, and 27.8° in an X-ray diffraction spectrum by CuK α-ray (D-form).
 7. The electrophotographic photoreceptor according to claim 1, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.7°, 16.3°, 24.2°, and 27.6° in an X-ray diffraction spectrum by CuK α-ray (E-form).
 8. The electrophotographic photoreceptor according to claim 1, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.7°, 8.2°, 11.1°, 12.4°, 13.3°, 15.3°, 18.5°, 18.8°, 22.1°, 22.5°, 25.5°, 27.0°, 28.7°, 29.1°, and 29.4° in an X-ray diffraction spectrum by CuK α-ray (F-form).
 9. The electrophotographic photoreceptor according to claim 1, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.4°, 9.9°, 12.5°, 12.9°, 16.1°, 18.5°, 21.9°, 22.2°, 24.0°, 25.1°, 25.8°, and 28.2° in an X-ray diffraction spectrum by CuK (x-ray (G-form).
 10. The electrophotographic photoreceptor according to claim 1, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.6°, 16.4°, 25.1°, and 26.6° in an X-ray diffraction spectrum by CuK α-ray (H-form).
 11. The electrophotographic photoreceptor according to claim 1, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 6.5°, 13.1°, 19.0°, 19.7°, 25.4°, and 26.3° in an x-ray diffraction spectrum by CuK α-ray (I-form).
 12. An electrophotographic photoreceptor which has a conductive substrate, and a photoconductive layer on the conductive substrate, wherein the photoconductive layer includes a μ-oxo-gallium phthalocyanine dimer as a charge generator, wherein said μ-oxo-gallium phthalocyanine dimer is selected from the group consisting of:a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 6.8°, 12.9°, 19.0°, 19.6°, 20.3°, 25.5°, 25.9°, and 26.9° in an X-ray diffraction spectrum by CuK α-ray (A-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.1° in an X-ray diffraction spectrum by CuK α-ray, and shows no clear peak other than 7.1° (Amorphous-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 8.1°, 8.7°, 9.2°, 10.4°, 15.1°, 15.9°, 17.0°, 21.7°, 22.3°, 22.9°, 24.3°, 28.8°, 29.4°, and 30.5° in an X-ray diffraction spectrum by CuK α-ray (B-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.7°, 16.0°, 24.9°, and 26.3° in an x-ray diffraction spectrum by CuK α-ray (C-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.3°, 8.8°, 22.6°, 25.5°, and 27.8° in an X-ray diffraction spectrum by CuK α-ray (D-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.7°, 16.3°, 24.2°, and 27.6° in an X-ray diffraction spectrum by CuK α-ray (E-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.7°, 8.2°, 11.1°, 12.4°, 13.3°, 15.3°, 18.5°, 18.8°, 22.1°, 22.5°, 25.5°, 27.0°, 28.7°, 29.1°, and 29.4° in an X-ray diffraction spectrum by CuK α-ray (F-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.4°, 9.9°, 12.5°, 12.9°, 16.1°, 18.5°, 21.9°, 22.2°, 24.0°, 25.1°, 25.8°, and 28.2° in an X-ray diffraction spectrum by CuK α-ray (G-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.6°, 16.4°, 25.1°, and 26.6° in an X-ray diffraction spectrum by CuK α-ray (H-form), and a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 6.5°, 13.1°, 19.0°, 19.7°, 25.4°, and 26.3° in an x-ray diffraction spectrum by CuK α-ray (I-form).
 13. The electrophotographic photoreceptor according to claim 12, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 6.8°, 12.9°, 19.0°, 19.6°, 20.3°, 25.5°, 25.9°, and 26.9° in an X-ray diffraction spectrum by CuK α-ray (A-form).
 14. The electrophotographic photoreceptor according to claim 12, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.1° in an X-ray diffraction spectrum by CuK α-ray, and shows no clear peak other than 7.1° (Amorphous-form).
 15. The electrophotographic photoreceptor according to claim 12, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 8.1°, 8.7°, 9.2°, 10.4°, 15.1°, 15.9°, 17.0°, 21.7°, 22.3°, 22.9°, 24.3°, 28.8°, 29.4°, and 30.5° in an X-ray diffraction spectrum by CuK α-ray (B-form).
 16. The electrophotographic photoreceptor according to claim 12, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.7°, 16.0°, 24.9°, and 26.3° in an X-ray diffraction spectrum by CuK α-ray (C-form).
 17. The electrophotographic photoreceptor according to claim 12, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.3°, 8.8°, 22.6°, 25.5°, and 27.8° in an X-ray diffraction spectrum by CuK α-ray (D-form).
 18. The electrophotographic photoreceptor according to claim 12, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.7°, 16.3°, 24.2°, and 27.6° in an X-ray diffraction spectrum by CuK α-ray (E-form).
 19. The electrophotographic photoreceptor according to claim 12, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.7°, 8.2°, 11.1°, 12.4°, 13.3°, 15.3°, 18.5°, 18.8°, 22.1°, 22.5°, 25.5°, 27.0°, 28.7°, 29.1°, and 29.4° in an X-ray diffraction spectrum by CuK α-ray (F-form).
 20. The electrophotographic photoreceptor according to claim 12, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.4°, 9.9°, 12.5°, 12.9°, 16.1°, 18.5°, 21.9°, 22.2°, 24.0°, 25.1°, 25.8°, and 28.2° in an X-ray diffraction spectrum by CuK α-ray (G-form).
 21. The electrophotographic photoreceptor according to claim 12, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.6°, 16.4°, 25.1°, and 26.6° in an X-ray diffraction spectrum by CuK α-ray (H-form).
 22. The electrophotographic photoreceptor according to claim 12, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 6.5°, 13.1°, 19.0°, 19.7°, 25.4°, and 26.3° in an x-ray diffraction spectrum by CuK α-ray (I-form).
 23. A function separated-form electrophotographic photoreceptor which has a conductive substrate, a charge generating layer on the conductive substrate, and a charge transporting layer on the charge generating layer, wherein the charge generating layer includes a μ-oxo-gallium phthalocyanine dimer as a charge generator, wherein said a μ-oxo-gallium phthalocyanine dimer is selected from the group consisting of:a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 6.8°, 12.9°, 19.0°, 19.6°, 20.3°, 25.5°, 25.9°, and 26.9° in an X-ray diffraction spectrum by CuK α-ray (A-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.1° in an X-ray diffraction spectrum by CuK α-ray, and shows no clear peak other than 7.1° (Amorphous-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 8.1°, 8.7°, 9.2°, 10.4°, 15.1°, 15.9°, 17.0°, 21.7°, 22.3°, 22.9°, 24.3°, 28.8°, 29.4°, and 30.5° in an X-ray diffraction spectrum by CuK α-ray (B-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.7°, 16.0°, 24.9°, and 26.3° in an X-ray diffraction spectrum by CuK α-ray (C-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.3°, 8.8°, 22.6°, 25.5°, and 27.8° in an X-ray diffraction spectrum by CuK α-ray (D-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.7°, 16.3°, 24.2°, and 27.6° in an X-ray diffraction spectrum by CuK α-ray (E-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.7°, 8.2°, 11.1°, 12.4°, 13.3°, 15.3°, 18.5°, 18.8°, 22.1°, 22.5°, 25.5°, 27.0°, 28.7°, 29.1°, and 29.4° in an X-ray diffraction spectrum by CuK α-ray (F-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.4°, 9.9°, 12.5°, 12.9°, 16.1°, 18.5°, 21.9°, 22.2°, 24.0°, 25.1°, 25.8°, and 28.2° in an X-ray diffraction spectrum by CuK α-ray (G-form), a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.6°, 16.4°, 25.1°, and 26.6° in an X-ray diffraction spectrum by CuK α-ray (H-form), and a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 6.5°, 13.1°, 19.0°, 19.7°, 25.4°, and 26.3° in an x-ray diffraction spectrum by CuK α-ray (I-form).
 24. The function separated-form electrophotographic photoreceptor according to claim 23, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 6.8°, 12.9°, 19.0°, 19.6°, 20.3°, 25.5°, 25.9°, and 26.9° in an X-ray diffraction spectrum by CuK α-ray (A-form).
 25. The function separated-form electrophotographic photoreceptor according to claim 23, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.1° in an X-ray diffraction spectrum by CuK α-ray, and shows no clear peak other than 7.1° (Amorphous-form).
 26. The function separated-form electrophotographic photoreceptor according to claim 23, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 8.1°, 8.7°, 9.2°, 10.4°, 15.1°, 15.9°, 17.0°, 21.7°, 22.3°, 22.9°, 24.3°, 28.8°, 29.4°, and 30.5° in an X-ray diffraction spectrum by CuK α-ray (B-form).
 27. The function separated-form electrophotographic photoreceptor according to claim 23, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.7°, 16.0°, 24.9°, and 26.3° in an X-ray diffraction spectrum by CuK α-ray (C-form).
 28. The function separated-form electrophotographic photoreceptor according to claim 23, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.3°, 8.8°, 22.6°, 25.5°, and 27.8° in an X-ray diffraction spectrum by CuK α-ray (D-form).
 29. The function separated-form electrophotographic photoreceptor according to claim 23, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.7°, 16.3°, 24.2°, and 27.6° in an X-ray diffraction spectrum by CuK α-ray (E-form).
 30. The function separated-form electrophotographic photoreceptor according to claim 23, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.7°, 8.2°, 11.1°, 12.4°, 13.3°, 15.3°, 18.5°, 18.8°, 22.1°, 22.5°, 25.5°, 27.0°, 28.7°, 29.1°, and 29.4° in an X-ray diffraction spectrum by CuK α-ray (F-form).
 31. The function separated-form electrophotographic photoreceptor according to claim 23, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.4°, 9.9°, 12.5°, 12.9°, 16.1°, 18.5°, 21.9°, 22.2°, 24.0°, 25.1°, 25.8°, and 28.2° in an X-ray diffraction spectrum by CuK α-ray (G-form).
 32. The function separated-form electrophotographic photoreceptor according to claim 23, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 7.6°, 16.4°, 25.1°, and 26.6° in an X-ray diffraction spectrum by CuK α-ray (H-form).
 33. The function separated-form electrophotographic photoreceptor according to claim 23, wherein said μ-oxo-gallium phthalocyanine dimer is a μ-oxo-gallium phthalocyanine dimer having a novel polymorph which shows diffraction peaks at a Bragg angle (2 θ±0.2°) of 6.5°, 13.1°, 19.0°, 19.7°, 25.4°, and 26.3° in an x-ray diffraction spectrum by CuK α-ray (I-form). 